Heating device and the like



June 28, 1938. R. REICHMANN HEATING DEVICE AND THE LIKE Original Filed July 14, 1933 k fi x h Patented June 28, 1938 UNITED STATES HEATING DEVICE AND THE Reinhold Reichmann, Berlin,

to Siemens & Halske,

Germany, assignor Aktlengesellschaft, Sic-1 mensstadt, near Berlin, Germany, a corpora- German tion of Original a 3 Claims.

This invention relates to heating devices and particularly to heating elements and is a division of my ctr-pending application Serial No. 680,455, filed July 14, 1933 which has matured into Patent No. 2,091,107 dated Aug. 24, 1937.

It is the principal aim of my invention disclosed herein to obtain an improved heating device by the provision of a substantially perfectprotection for heating conductors and the like. The conductors are disposed'in a protecting sheath of refractory material" which does not undergo any reactions with the conductors and furnishes a gas-tight enclosure therefor and a compact unitary structure therewith. The need for such protection of a heating conductor or the like will be apparent from a brief consideration of the following facts relating to the prior art.

Taking, for example, the case of high temperature electric furnaces, .it was possible in the past to construct such furnaces only up to reliable operating temperatures of around 1100 C. without using any particular neutral gas. It should be considered that even highly refractory metals oxidize very rapidly in contact with air at high temperatures so that the resistor or heating elements which are usually thin aregsubjected to rapid deterioration. Higher temperatures may be obtained, for example, by the use of platinum as resistance material. However, platinum has not come into extensive use due to its prohibitive cost and also because it has the tendency to volatilize at high loads. It is therefore subject to recrystallization and as a heating conductor has only a limited durability.

It has also been proposed to produce heating elements for high temperatures by surrounding the heating conductors with finely granulated argillaceous earth, placing the resulting structures into a suitable mold and baking the envelope of argillaceous earth to form a protecting sheath around the conductor by rent thru the same. However, it is impossible to provide in this manner for a perfect sintering of the argillaceous earth, particularly when it is desired that the protecting sheath should be of suificient thickness as might be required in a given structure. Moreover, the powdered material which is loosely distributed over the heating element proper does not sinter firmly enough so as to provide a gas-tight envelope for. the conductor. Consequently, heating elements made in this manner can not be reliably employed for many purposes, for example, for heating liquids or fuse baths wherein detrimental gases are developed. It is not even possible to produce in passing an electric cur-- application July 14, 1933, Serial No. Divided and this application March 1935, Serial No. 12,039.

In Germany July the above intimated manner a protecting sheath that fits the heating conductor tightly. Either an interstice results which is detrimental-to the heat transifer and promotes the entrances! air or gases at the ends of the sheath, or the sheath does not contract during the sintering to the desired extent and the result is the formation of cracks.

In accordance with my invention, a heating device is produced characterized by a substantially perfect protection of the heating eonductor.-

The heating conductor or resistance material consists as a ruleof a metal or a metal compound which may be suitably surrounded, for example, by a ceramic method, with a protecting sheath or envelope of refractory material which may be sintered together with the corresponding resistor or conductor, for example, in a baking furnace in an inert atmosphere at a temperature above 1600 C. until the protecting sheath is completely compact and in gas-tight and firm engagement with the heating conductor. Any suitable method for applying the protecting sheath or envelope on the conductor or resistor may be employed. By referring to ceramic methods, such methods are to be understood which are employed in theceramic industry for the manufacture oi shaped bodies consisting, for example, in rendering the ceramic material moldable orplastic by the addition of suitable binding agents or forming a moldabie slip by'adding a suitable electrolyte and/or suitably presslng or forming the resulting mixture to obtain the desired shapes or bodies.

I prefer to employ highly refractory metallic such as-tungsten, molybdenum, or alloys of tung sten or molybdenum for this purpose. An alloy of tungsten and molybdenum has proved to be particularly suitable since its coemcient of expansion is approximately equal to that of the protecting sheath which may in this erably consist of beryllium oxide. Detrimental changes in the heating resistor which may result case prefarranged for operation at temperatures ranging around and/or above 1600 C. which corresponds to the aintering temperature applied in the example described previously.

- Changes may be carried out, if desired, within the scope and spirit of the appended claims.

I claim as my invention:

1. As an article of manufacture, a heating unit for an electric furnace or the like, said unit comprising a metallic heating section of uniform diameter, said heating section having a terminal section at each end thereof of enlarged diameter, a helical member wound around each terminal section, and an impervious sheath of sintered metallic oxide covering said heating section, said helical members and a substantial portion of each terminal section, said sheath tightly gripping said terminal sections and helical members due to shrinkage in the sintering operation and serving thereby to seal the entire heating section against the entrance of gases.

2. As an article of manufacture, a heating unit for an electric furnace or the like in which the heating units are exposed to the air and relatively high temperatures on the order of 1600 C. are attained, said unit comprising a metallic rod structure having a section at each end of enlarged diameter and a heating section of smaller diameter between, each enlarged section having a helical member wound around it for a portion of its length, and a sheath of metallic oxide sintered on said rod by the application of heat, said sheath covering also the said helical members at the ends of said rod structure and being effective to seal the entire heating section against the entrance of gases.

3. An electrical heating unit for producing in normal operation without the use of any protective gaseous medium temperatures ranging around 1600 C., said unit comprising a tungsten resistor, a terminal at each end of said resistor, a helical member wound around each terminal, and insulating'means for enclosing said resistor gas-tight, said insulating means being formed of highly sintered aluminum oxide placed about said resistor and entering the grooves in said helical members, thereby forming a unitary gas-tight enclosure for said resistor.

REINHOLD REICHMANN. 

